It is known to use a local computer or similar device to interact with a physically remote computer. For the individual user, one common scenario is to help troubleshoot the computer of a distant less-technically-savvy relative. Sitting at your desk in Baltimore, remote computing allows a user to take control of a relative's PC in California and show them how to use a new software package by actually doing it from your PC in Baltimore. A very common business application is in remote system administration, where it is used to allow administrators to take control of employee machines to diagnose and fix problems. In all scenarios, key presses, mouse movements, and mouse clicks are sent from the local computer to the remote computer to effect changes on the remote computer. A continually updated copy of the remote computer's display is shown in a window on the local computer. Accordingly, it appears to a user that they are sitting in front of the remote computer even though it is at a different location.
The continually updated copy is achieved by encoding pixel data describing the contents of the remote computer's display and transmitting this data, or any changes in this data, to the local computer. There are many ways of achieving this encoding. At one end of the range, there is Raw encoding which has no data compression and thus requires minimal CPU overhead at the remote computer but is only suitable for fast networks because of the large volume of data to be transmitted. At the other end of the range, there is high compression encoding (e.g. Run Length Encoding RLE or variations thereof) which offer better compression and are suitable for slower networks but require higher CPU overhead. These standard encodings are all lossless and thus the display on the local computer is an exact representation of the display on the remote computer.
Typically the display on the remote computer comprises a mixture of text and image data. The amount of image data has increased in recent years to include more images and video; and because of the trend towards semi-transparent and blurred window frames, and highly textured or graduated color backgrounds and fill patterns.
There is a strong temporal element to remote computing; the algorithms producing and transmitting the continually updated copy of the remote computer display have to be fast enough to keep up with the changes on the remote computer without falling behind. A bottleneck may arise from the encoding time, the data communication time, or the decoding time.
The present applicant has recognized the need for an improved encoding.